Conventional horn switches for automobiles were traditionally mounted atop a center hub of a steering wheel. However, attempts were eventually made to boldly style the center features of a steering wheel which lead to designs having a molded and padded center cover alongside which a pair of rabbit ear horn switches depend, one extending from each side. With the introduction of driver air bag modules, it also became desirous to mount air bag modules at the center of a steering wheel, so the previously implemented center cover feature was also carried forward for use with air bags. Therefore, it remained necessary to continue mounting horn switches either on rabbit ears, or to provide the horn switches on an outer edge of the air bag module cover, and as a result various related designs are presently in use. However, many users desire placement of both the air bag module and horn switch at the center of the steering wheel. Center placement of the horn switch allows a user to quickly and accurately trigger a vehicle horn no matter what angular position the steering wheel is in. Furthermore, many users desire accessory switches which are incorporated within the design surface of the air bag cover. As a result, several attempts have also been made to incorporate switches directly into the design of an air bag module, including horn switches that activate a horn by pressing a center portion of the module.
One design features an air bag module that is mounted with resilient springs to a steering wheel hub. A contact horn switch, which is provided between the module and hub, is activated by depressing the module against the hub to compress the springs which closes a circuit and activates a vehicle horn. However, the air bag actually "floats" above the steering wheel hub on the springs, requiring a significant increase in the number of parts needed to assemble the module to the hub, and furthermore increasing the cost and complexity of assembly. Additionally, when accessory switches are also provided on the module, activation of the accessory switches by a user caused by depressing the switches might also inadvertently depress and activate the horn switch.
Another design features a membrane switch molded directly into a cover for an air bag module. The cover, which is molded from a resilient material, is manually depressed by a user in order to activate the switch. The membrane switch can reduce overall cost, size of the module cover within the steering wheel hub, and ease of module assembly. However, the cover must be flexible in order to allow switch activation, and for cases where one switch is mounted in close proximity to adjacent switches on a cover, it becomes difficult to assure discrete activation of an individual button since activation of one switch will deform the cover over a surrounding region. As a result, if the switches are too close together, a nearest neighbor switch might be inadvertently activated.
Finally, redundant accessory switches have recently been added to steering wheels in order to allow a driver to activate various vehicle features directly from the steering wheel. For example, radio controls, cruise controls, cellular telephone buttons, and air conditioning buttons have all been located on separate switches attached to a steering wheel. In most cases, the switches are redundant with switches found on the vehicle instrument panel, and are added to provide driver convenience and safety. Usually, the switches are attached to the steering column adjacent the air bag module. For example, the switches can be attached to a molded surface of the wheel surrounding the mounted air bag, preferably along the inner spokes of the steering wheel. Alternatively, the switches can be provided directly on the air bag module along an outer peripheral portion of the module, but away from cover deployment doors as well as the trajectory path of an inflating air bag as the bag deploys through the center of the air bag module. However, the switches are typically formed from a number of separate pieces that mount through openings in the cover, and as a result they complicate construction and assembly of the module.